Simultaneous measurements of in situ Raman spectroscopy and cyclic voltammetry have been carried out for thin film electrodes of LixCoO2 in propylene carbonate containing 1 M LiClO4. The Raman lines of 485 and 587 cm(-1) observed at LixCoO2 electrodes were attributed to the A(1g) and E-g modes of the LiCoO2, respectively. The Raman intensity of two lines changed drastically during the insertion/extraction of lithium ions. This effect can be explained by the reduction of the optical skin depth due to the conductivity change of LixCoO2. Phase transition from Raman-active phase to Raman-inactive phase is also conceivable.